Cytogenetic analysis was successful in 32 of 37 fetuses and children whose peripheral leukocytes were cultured between 2 and 288 hours after death. Viable leukocytes from older infants and children were obtained tip to 48 hours postmortem and as late as 117 hours postmortem from young fetuses. Blood from infants whose body temperatures remained at 25°C or greater for prolonged periods after death usually failed to grow, as did cardiac blood after exposure to hypertonic medications used for resuscitation. Bacterial or fungal contamination of blood did not prevent successful cultures, and chromosome breakage compared favorably with that in routine cultures.